The purpose of this contract is to characterize the in vivo chemical toxicity in laboratory animals associatedwith short term exposures generally ranging from two to twenty-six weeks. The Contractor may be required to perform in vitro studies for further characterization of toxicty. The studies performed under this contract will identify possible target organ(s) toxicity, similarities and differences in sensitivity between sexes and species of animals and dose response relationships. The data from these studies will also be used by the National Toxicology Program for establishment of dose levels of chemicals for subsequent long-term carcinogenicity.